Preface to the English Edition. xvii 



darkness of ignorance, there appeared at the same 

 time some other researches in which this doctrine 

 itself became the object of investigation, and 

 which were undertaken with a view to establish it 

 more securely. 



To this latter class of work belong the 

 " Studies " in the present volume. 



It will perhaps be objected that the theory of 

 descent has already been sufficiently established 

 by Darwin and Wallace. It is true that their 

 newly-discovered principle of selection is of the 

 very greatest importance, since it solves the riddle 

 as to how that which is useful can arise in a purely 

 mechanical way. Nor can the transforming in- 

 fluence of direct action, as upheld by Lamarck, be 

 called in question, although its extent cannot as yet 

 be estimated with any certainty. The secondary 

 modifications which Darwin regards as the conse- 

 quence of a change in some other organ must 

 also be conceded. But are these three factors 

 actually competent to explain the complete trans- 

 formation of one species into another ? Can they 

 transform more than mere single characters or 

 groups of characters ? Can we consider them as 

 the sole causes of the regular phenomena of the 

 development of the races of animals and plants ? 

 Is there not perhaps an unknown force underlying 

 these numberless developmental series as the true 

 motor power a "developmental force" urging 

 species to vary in certain directions and thus 



